Sounds like Bayesian reasoning? I don't think that your argument 1-3 works unless we shared all the facts and had the same priors. We could both be perfectly rational and have different priors but be exposed to the same facts and have different resulting posterior probabilities for different conclusions.
Sometimes the epistemic reasons weigh up multiple beliefs as precisely equal
Epistemic reasons aren't precisely commensurable. Then sometimes there may be multiple beliefs for which no other belief has more reason-support, despite such beliefs not having precisely the same amount of support.
Sounds like Bayesian reasoning? I don't think that your argument 1-3 works unless we shared all the facts and had the same priors. We could both be perfectly rational and have different priors but be exposed to the same facts and have different resulting posterior probabilities for different conclusions.
3 can be false if either...
Sometimes the epistemic reasons weigh up multiple beliefs as precisely equal
Epistemic reasons aren't precisely commensurable. Then sometimes there may be multiple beliefs for which no other belief has more reason-support, despite such beliefs not having precisely the same amount of support.